JPS6357808B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a constant current drive circuit including a feedback system used when passing a constant current to a load such as a motor, and its purpose is to provide stable constant current drive. It is an object of the present invention to provide a constant current drive circuit which is possible and suitable for integration.

Generally, in a constant current drive circuit including a feedback system, when a constant current is to flow through a load such as a motor, a low resistance is connected in series between the load and the power supply or ground, so that the voltage across it remains constant. A method of driving a load is known. Figure 1 shows part 1.
Give an example. Here, the diode D1 is used to correct the base-emitter voltage V _BE of the transistor Q1, and it is assumed that the forward drop voltage V _D1 and the V _BE of the transistor Q1 are equal to each other, and that the transistor Q1 and the current amplifier 1 (first Assuming that the current amplification factor of the transistor Q1 (the specific configuration of which is shown in Figure b) is sufficiently large and ignoring the base current of transistor Q1, I _L = (R _C /R _CS )・I _C ...(1), and the command input current By giving I _C , the load R _L
can be driven with a constant current _IL . The operation of this circuit is such that when current I _C increases, voltage VQ _1B decreases, current I _A increases, and current I _L increases accordingly. Conversely, when current I _C is decreased, current I _L is also decreased. Then, voltages VQ _1B and VQ _1E are balanced, resulting in an equilibrium state. However, in order to satisfy the above assumption, the current of diode D1 and transistor Q
It is necessary to keep the ratio of the emitter currents of 1 to 1 constant, and it is difficult to satisfy equation (1) over a wide range of load currents I _L .

Therefore, in order to solve the above-mentioned problem, it is conceivable to use a differential amplifier that operates up to the power supply as a comparison circuit. Fig. 2 shows one example, in which transistors Q ₂ and Q ₃ are a differential amplifier as a comparison circuit,
Transistors Q ₄ and Q ₅ are a bias circuit driven by a constant current source I _B , and transistors Q ₆ and Q ₇ are a current mirror circuit as an active load.
R _L is connected within a feedback system consisting of a current amplifier 2 (same configuration as shown in FIG. 1b) and a transistor Q ₃ connected to the collectors of transistors Q ₅ and Q ₇ . When a differential amplifier that operates up to the power supply is used as a comparison circuit, the current amplifier 2
By increasing the amplification factor sufficiently and reducing its input current, it is possible to reduce the offset caused by the error in the base-emitter voltage _VBE of transistor _Q3 . The operation of this circuit is that when the current I _C increases, the voltage VQ _2B decreases and the current IQ _2E (=
IQ _(4C ) decreases. Along with this, the current IQ _7C also decreases, so that the current I _A increases and the current I _L increases.
Conversely, when current I _C is decreased, current I _L is also decreased.
Then, voltages VQ _2B and VQ _3B are balanced, resulting in an equilibrium state. However, in this circuit, the feedback system as a whole tends to oscillate. In other words, since the operating current of the comparator varies greatly depending on the minute current source I _B that provides the bias and the parameter hfe of transistors _Q4 and Q5, it becomes difficult to maintain the symmetry of the collector currents of transistors Q4 and _Q5 . It was hot.

The present invention eliminates such conventional drawbacks, and the present invention will be described below with reference to drawings of embodiments.

FIG. 3 shows one embodiment of the invention. In FIG. 3, transistors Q ₈ , Q ₉ , and Q ₁₀ constitute a Wilson-type current mirror circuit that operates as a current source, and transistor Q ₈ is supplied with a command input current I _C.
The emitter of transistor Q ₉ is connected to the power supply via resistor R _C and the emitter of transistor Q 9 is connected to the power supply via resistors R ₁ and R _CS . Transistors Q ₁₂ and Q ₁₃ form a current mirror circuit that sinks current, and the collector of transistor Q ₁₂ is a transistor.
To the collector of Q ₈ , the collector of transistor Q ₁₃ is connected to the collector of transistor Q ₁₀ .
Transistor _Q11 is a booster for a current mirror circuit that sinks current, and its base and emitter are connected to the collector and base of transistor _Q13 , and its collector is connected to the power supply. The load R _L has one end connected to the above resistance R ₁ and R _CS
The other end is grounded via the current amplifier 3 (the specific configuration of which is shown in FIG. 3b) and the transistor _Q14 , and the base of the transistor _Q14 is connected to the transistor _Q12. ，
Commonly connected to the base of Q ₁₃ .

In this case, assuming that the current mirror circuit operates ideally, the operation of the entire circuit will be explained as follows using the equivalent circuit shown in FIG. 3c. That is, when the current I _C is increased, the voltage VQ _8E decreases,
The current IQ _8C decreases and therefore the current I increases. Along with this, the currents IQ _9C , IQ _12C , and IQ _14C increase,
The current _IL increases. Conversely, when current I _C is decreased, current I _L also increases. And voltage VQ _8E and VQ _9E
When the two are balanced, an equilibrium state is reached. In equilibrium, the voltage between the emitter of transistor _Q8 and V _CC is
Assuming VQ _8E , VQ _8E = (I _C + IQ _8C )・R _C Also, assuming the voltage between the emitter of transistor Q ₉ and V _CC as VQ _9E , VQ _9E = (IQ _9C + I _L )・R _CS + IQ _9C・In the R ₁ equilibrium state, VQ _8E = VQ _9E , so (I _C + IQ _8C )・R _C = (IQ _9C + I _L )・R _CS +IQ _9C・R ₁ I _C・R _C +IQ _8C・R _C = IQ _9C・R _CS +I _L・R _CS +IQ _9C・R _1Here , set IQ _8C = IQ _9C →I ₈ , I _L・R _CS =I _C・R _C +I ₈・R _C −I ₈・R _CS −I _{8 ・}R ₁ = I ₈・(R _C −R _CS −R ₁ )＋I _C・R CHere, if R _CS ≪R _C , R ₁ , then =I ₈・(R _C −R ₁ )+I _C・R _C ∴I _L = 1/R _CS・{I ₈・(R _C −R ₁ )＋I _C・R _C } ...(2) In particular, if R _C = R ₁ , I _L = R _C /R _CS・I _C ...(3), and formula (1) can be satisfied. and,
The current amplifier 3 uses the transistor Q ₁₄ and is commonly connected to the bases of the transistors Q ₁₂ and Q ₁₃ , that is, the base output of the transistors Q ₁₂ and Q ₁₃ is given, so the symmetry between I ₈ and I ₉ is maintained. and stable constant current drive can be performed.

FIG. 4 shows another embodiment of the present invention. The difference from FIG. 3 is that a differential amplifier consisting of transistors Q ₁₅ and Q ₁₆ is used as a comparison circuit, and the base of transistor Q ₁₅ is connected via a resistor R _C. to the power supply, connect the base of transistor _Q16 to resistor R _CS and load R _L
This means that it is connected to the connection point of . In this case, if the current mirror circuit operates ideally, I ₁₄ =
I ₁₅ , the base-emitter voltage V _BE of transistors Q ₁₄ and Q ₁₅ is compensated, and I _L = R _C /R _CS · I _C ...(4), which satisfies equation (1). . and,
In this case, it is particularly effective when the load current is small, and stable constant current driving can be performed.

In the above embodiment, a Wilson type current mirror circuit that operates as a constant current source is used.
This may be a normal current mirror circuit, i.e., omitting the transistor _Q10 , and may also be
Although a booster is used in the current mirror circuit that performs a current sinking operation, this booster may be a normal current mirror circuit, that is, one that is directly connected to the base and collector of the transistor _Q13 .

Also, transistors _Q8 to _Q16 are each NPN
Needless to say, may be replaced with PNP, and PNP may be replaced with NPN. In this case, the current mirror circuit that operates as a current source is replaced with a current sink operation, and the current mirror circuit that operates as a current sink is replaced with a current source operation.

As described above, according to the present invention, good constant current drive is possible, and in this case, all that is required is a resistor,
It is not the absolute value of hef etc. but their relative precision,
This is particularly effective when used as an integrated circuit.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a basic constant current drive circuit, Figure 2 is a circuit diagram of a constant current drive circuit using a differential amplifier, and Figure 3 is a circuit diagram of a constant current drive circuit using the present invention.
FIG. 4 is a circuit diagram showing another embodiment of a constant current drive circuit using the present invention. R _C ...Standard resistance, R _CS ...Current detection resistor, I _C ...
...Command current, I _L ...Drive current, Q ₈ to Q ₁₆ ... Transistor, 3... Current amplifier, R _L ... Load, R ₁
……resistance.

Claims (1)

[Claims] 1. A current mirror circuit that operates as a current source, and an output of the current mirror circuit that operates as a current source and its command input are connected, and a command input of the current mirror circuit that operates as a current source and its command input are connected. a current mirror circuit that performs a current sink operation to which a mirror output is connected; a resistor connected between a power source and a first terminal connected to the emitter or collector of a command side transistor of the current mirror circuit that performs a current source operation; A resistor is connected between the second terminal connected to the emitter or collector of the output side transistor of the current mirror circuit operating as a current source and the power supply, and the voltage drop due to the current sucked from the first terminal is The present invention is characterized by having a comparison circuit configured to compare the voltage between the power supply and the second terminal, and output the error from a third terminal connected to a common base of the current mirror circuit that performs the current sinking operation. constant current drive circuit. 2 Use a differential amplifier instead of a resistor, connect the base of one transistor to the first terminal, connect the base of the other transistor to the second terminal, and calculate the voltage between the power supply and the first terminal and the power supply. 2. The constant current drive circuit according to claim 1, wherein the voltage between the second terminals is compared and the error thereof is output from the third terminal.